The gunman's hotel room was on the 32nd floor of the Mandalay Bay hotel with a flawless view of the concert grounds where more than 20,000 people had gathered some 400 yards away for the Route 91 Harvest Musical Festival before Paddock launched his attack.

Kiwi songstress Lorde, Chance the Rapper and United Kingdom rock band Muse were among the headliners at the September 22-24 festival.

A man named Stephen Paddock reserved a room at the Blackstone Hotel, in Chicago, at the same time as the Lollapalooza music festival was taking pace in the IL city.

While other mass killers have left a trail of plain-sight clues that helped investigators quickly understand what drove them to violence, Paddock led a low-key, private life.

In an interview airing on 60 Minutes in the USA, three police officers who were in the Mandalay Bay hotel room will reveal new details about what they discovered. "We don't know yet", he said.

"We have been down each and every single one of these paths trying to determine why". But as investigators continue to dig into the 64 year-old millionaire real estate investor's movements and purchases in the months, days and hours leading up to his insane rampage, a more detailed picture has emerged about the meticulous planning that went into Paddock's unthinkable actions.

She said: "ISIS has rarely claimed attacks that were not by either their members or sympathisers".

His girlfriend, Marilou Danley, told FBI agents Wednesday that she had not noticed any changes in his mental state or indications he could become violent, the federal official said.

"He never said anything to me or took any action that I was aware of that I understood in any way to be a warning that something terrible like this was going to happen", she said in a statement read by her lawyer.

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